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Publication numberUS5661293 A
Publication typeGrant
Application numberUS 08/547,289
Publication dateAug 26, 1997
Filing dateOct 24, 1995
Priority dateNov 7, 1994
Fee statusPaid
Also published asCN1128357A, DE4439759C1
Publication number08547289, 547289, US 5661293 A, US 5661293A, US-A-5661293, US5661293 A, US5661293A
InventorsRoland Ziegler, Rolf Lindner
Original AssigneeSiemens Aktiengesellschaft
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Photodiode array with photodiode/extraction diode combinations with dark current thereof regulated to zero
US 5661293 A
Abstract
A solid-state radiation detector, including a photodiode array, is suitable for use in computed tomography, with the dark current of the photodiodes being compensated. The compensation is accomplished by an adjustable voltage source connected to the photodiode, the voltage of the adjustable voltage source being set by a regulator so that the dark current becomes zero. The regulator receives a signal corresponding to the dark current from a measured value transducer in the form of a current-driven voltage source. The voltage supplied by the adjustable voltage source to the photodiode is maintained constant while x-rays are incident on the overall detector which cause illumination of the photodiode.
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Claims(1)
We claim as our invention:
1. A solid-state radiation image detector comprising:
a photodiode array containing a plurality of photodiodes and a plurality of extraction diodes, said extraction diodes respectively connected to said photodiodes thereby forming a plurality of photodiode/extraction diode combinations, each photodiode/extraction diode combination having a dark current associated therewith;
an adjustable voltage source connected to each photodiode/extraction diode combination, said voltage source having a voltage associated therewith;
means for generating a signal proportional to the dark current; and
regulator means supplied with said signal proportional to the dark current for regulating the voltage of said adjustable voltage source dependent on said signal proportional to the dark current for maintaining a voltage across the photodiode/extraction diode combination connected to the adjustable voltage source constant during optical irradiation of that photodiode for regulating said dark current to zero.
Description
BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a photodiode array of the type suitable for use as a radiation detector.

2. Description of the Prior Art

Solid-state radiation detectors formed by a photodiode array are employed in x-ray computed tomography. Scintillators are disposed in front of the photodiodes of the array, the scintillators converting incident x-rays into visible light. The visible light is converted by the photodiodes into a corresponding electrical signal. In order to improve the signal quality, an extraction diode can be connected between each two neighboring photodiodes. The dark current of the photodiodes is thus dependent on the temperature and the Voltage of the extraction diodes. The voltage for the extraction diodes is fixed for all of the extraction diodes, so as to compensate for the effects of the direct conversion of x-rays in the photodiodes into a contribution to the electrical output signal, as well as to compensate for optical cross-talk between photodiodes.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a photodiode array of the type described above wherein improved dark current compensation is achieved.

The above object is achieved in accordance with the principles of the present invention in a photodiode array having a number of individual photodiodes, with a voltage source connected to the photodiodes so that an adjustable voltage is present across each individual diode. The adjustable voltage is set by a regulator which receives a signal which is proportional to the dark current from a transducer which measures a parameter which is representative of the dark current. The voltage across each photodiode is adjusted as necessary during exposure of a photodiode to incoming radiation, so as to maintain the voltage constant during the exposure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram of a photodiode array and operating circuitry constructed in accordance with the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the photodiode array and operating circuitry shown in the drawing, a photodiode 1 has extraction diodes 2 allocated thereto. The extraction diodes 2 are connected in parallel, and are followed by a further photodiode constructed on the same substrate as the photodiode 1 and the extraction diodes 2. The extraction diodes 2 are connected across an extraction voltage source 3. The photodiode 1 produces an electrical signal in a known manner as a result of light being incident thereon which is produced by, for example, a scintillator which has been exposed to x-rays. The electrical signal generated by the photodiode 1 is supplied to a data processing system (not shown) via a floating ground amplifier stage 4 containing one or more pairs of connected amplifiers such as 4a and 4b. The output of the amplifier stage 4 leads to a current meter in the processing stage.

A regulator 5 is connected to a current-driven voltage source 6 functioning as a measured value converter. The regulator 5 and the current-voltage source 6 are both connected to a variable voltage source 7, connected to the amplifier stage 4 for compensating the dark current.

The dark current can be completely compensated by applying the voltage of the voltage source 7 to the photodiode 1 via the amplifier stage 4. The current-driven voltage source 6 generates a signal proportional to the dark current which is supplied to the regulator 5. The regulator 5 sets the voltage of the variable source 7 and thereby compensates the dark current. The regulator 5 has a hold function (time t<2 min.). The voltage of the variable voltage source 7 must be maintained constant while x-rays are incident on the scintillator and the light generated thereby illuminates the photodiode 1. A hold signal is supplied at an input 8 to the regulator 5 when this occurs.

In a scintillator-photodiode detector, the automatic single-channel regulation shown in the drawing compensates for the dark current, and thus permits the full dynamic range of the photodiode 1 to be utilized. The circuit also renders the overall detector substantially insensitive to fluctuations in operating temperature, and serves to "level" temperature differences which may arise locally in individual detector areas. The circuit also prevents relatively small fluctuations in the extraction voltage from having any influence on the detector operation. The circuit also significantly reduces the influence of statistical scatter in the electrical properties of the various photodiodes 1 which are used within the array, and also minimizes the impact of statistical scatter in the properties of overall arrays. The circuit saves time in the overall detection procedure by avoiding the need to make repeated offset measurements, each of which has a measurement time associated therewith.

The automatic single-channel regulation disclosed herein thereby assures stable electrical separation of the individual channels, results in an optimum reduction of the direct conversion, and reliably produces a stable offset measurement thereby precluding the need to undertake such an offset measurement before each exposure.

Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3891857 *Feb 22, 1974Jun 24, 1975Aga AbDevice for the non-contact length measurement of objects
US4341956 *Mar 3, 1981Jul 27, 1982Pfizer, Inc.Apparatus and method for compensating the dark current photoelectric transducers
US4714827 *Jan 13, 1986Dec 22, 1987Nippon Soken, Inc.Photo-electric conversion device with dark current compensation
US4916307 *Dec 12, 1988Apr 10, 1990Fuji Electric Co., Ltd.Light intensity detecting circuit with dark current compensation
US4933543 *Sep 25, 1987Jun 12, 1990Chesley F. CarlsonDark signal compensation for diode arrays
US5296697 *Aug 10, 1992Mar 22, 1994Parkervision, Inc.Detection circuit for maintaining constant signal transfer characteristics of a light-sensitive detector
DE3604971A1 *Feb 17, 1986Aug 20, 1987Messerschmitt Boelkow BlohmPhotosensoreinrichtung mit dunkelstromkompensation
Non-Patent Citations
Reference
1"Method of Compensating Dark Current Photodiode Arrays", Korth, IBM Technical Disclosure Bulletin, vol. 22, No. 8B, Jan. 1980.
2 *Method of Compensating Dark Current Photodiode Arrays , Korth, IBM Technical Disclosure Bulletin, vol. 22, No. 8B, Jan. 1980.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5949842 *Oct 10, 1997Sep 7, 1999Analogic CorporationTo perform an air calibration of a computed tomography scanning system
US5970113 *Oct 10, 1997Oct 19, 1999Analogic CorporationComputed tomography scanning apparatus and method with temperature compensation for dark current offsets
US6256404Oct 10, 1997Jul 3, 2001Analogic CorporationComputed tomography scanning apparatus and method using adaptive reconstruction window
US6366636Mar 3, 2000Apr 2, 2002Hitachi, Ltd.X-ray sensor signal processor and X-ray computed tomography system using the same
US6925143Jun 10, 2004Aug 2, 2005Hitachi, Ltd.X-ray sensor signal processor and X-ray computed tomography system using the same
US6928138Jun 10, 2004Aug 9, 2005Hitachi, Ltd.X-ray sensor signal processor and X-ray computed tomography system using the same
US6975700Jun 10, 2004Dec 13, 2005Hitachi, Ltd.X-ray sensor signal processor and X-ray computed tomography system using the same
US7113563Oct 17, 2005Sep 26, 2006Hitachi, Ltd.X-ray sensor signal processor and X-ray computed tomography system using the same
US7260176Sep 13, 2006Aug 21, 2007Hitachi, Ltd.X-ray sensor signal processor and X-ray computed tomography system using the same
WO1999019716A1 *Sep 4, 1998Apr 22, 1999Analogic CorpCt target detection using surface normals
Classifications
U.S. Classification250/214.00C, 327/515, 250/214.00A
International ClassificationG01T1/29, G01T1/17, H01L31/10, G01T1/20
Cooperative ClassificationG01T1/17, G01T1/2928
European ClassificationG01T1/17, G01T1/29D1C
Legal Events
DateCodeEventDescription
Jan 15, 2009FPAYFee payment
Year of fee payment: 12
Jan 14, 2005FPAYFee payment
Year of fee payment: 8
Jan 16, 2001FPAYFee payment
Year of fee payment: 4
Oct 24, 1995ASAssignment
Owner name: SIEMENS AKTIENGESELLSCHAFT, GERMANY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:ZIEGLER, ROLAND;LINDNER, ROLF;REEL/FRAME:007733/0303
Effective date: 19951008